Joseph Byrne (21) went up to the boy as he was walking home from school and accused him of having his X-Box computer games console. When the victim said he didn't know anything about this Byrne used a blade to cut a 10cm slash down the side of the boy's face.

Garda Niall Minnock agreed with Michael O'Higgins SC, defending, at Dublin Circuit Criminal Court that Byrne comes from a very respectable family who had done their best by him and were standing behind him.

Counsel said that his client was off his medication when he carried out the attack. The victim has been left with a significant scar which is likely to be permanent, according to medical reports.

Byrne of Mac Uilliam Avenue, Tallaght, Dublin pleaded guilty to assault causing serious harm at Balbutcher Lane, Ballymun on February 4, 2014. He has 15 previous convictions including two for possession of knives.

Joseph Byrne Snr said his heart sank when gardai came to his door and told him what his son had done.

“I've often relived the morning. As a parent you automatically put yourself in the other parent's position. My heart sank,” he said.

He said his son was now back on medication and had made an unbelievable improvement and was back to the “old Joe that we knew and loved”.

He said he believed that his son now understood what he did, adding: “It's of some comfort to us as a family that he deeply regrets what took place that day”.

Mr Byrne Snr offered an apology to the victim and his family, who were present in court.

Mr O'Higgins asked Judge Desmond Hogan to allow Byrne to remain on bail pending sentence so that he could he could get the proper psychiatric supports necessary for him.

Judge Hogan said that Byrne was at a high risk of reoffending. He said the Probations Services would have assess to him while in prison before remanding him in custody for sentence next November.

Byrne had recently broken up with a girl and had left property including the X-box console there and he believed the victim now had the console.

He got out of a car as a passenger and walked to the victim and spoke to him before cutting him. He then got back into the car and the car moved off.

Blood was pouring from the victim's face and he ran towards a man in a nearby van and asked for help. He later received 36 stitches to close up the gaping and deep wound which ran from his ear down to his lip.

Mr O'Higgins said Byrne was not taking his medication at the time. His father said that because of this he would suffer extreme confusion, agitation and, from time to time, aggression.

“We were extremely concerned over him,” he said. He testified that he had made a couple of attempts to end his own life.

Byrne admitted being involved in a burglary in which three men rammed their way into a church.

He pleaded guilty to burglary at St Joseph's Church, Terenure on August 8, 2014.

Garda Lee Hunt told the court that a neighbour of the church saw a car driving erratically in the car park of the church before ramming the door until it broke.

When gardai arrived they heard loud banging noises from inside and found the men inside the church.

Glass panels had being broken and there was damage to the sacristy door but nothing was taken.

The total damage caused was €12,175.

Garda Hunt said the three men were all highly intoxicated. Byrne was on bail for the assault when he committed this burglary.